1. Technical Field
The present disclosure relates to an optical input device, in particular, to a tracking method of an optical input device and an optical input device using the same.
2. Description of Related Art
Correlation technique has been commonly used by optical input devices such as optical mice for aligning similar features between successive images captured i.e., a reference image and an input image (e.g., a compare image) captured subsequent to the reference image, so as to determine the relative motion (e.g., relative displacement and relative velocity) of the optical input device with respect to a work surface. The relative displacement and velocity tracked can be used for controlling the movement of a cursor on a display.
One of the conventional correlation techniques is to correlate the reference image and the compare image on a pixel by pixel basis using a two-dimensional cross-correlation. Even though the pixel by pixel correlation scheme in practice could yield accurate result but could be time consuming as it requires intensive computations. The optical input device generally is subject to specific technical constraints, particularly time and power constraints. Further, the related image processing must be performed within a very short period so that the movement of the optical input device can be indicated on the display in a manner which appears instantaneous to the user. Moreover, since optical input device is generally battery-powered, thus the longer the image processing time, the more power will be consumed.
Another conventional correlation technique is known as the block correlation scheme which computes correlation between the reference image and the compare image for a predefined correlation window, and obtains the peak correlation value. The block correlation scheme is more computationally efficient in comparison to the pixel by pixel correlation scheme. However, the peak found using the block correlation scheme sometimes may not be the real peak. That is, the peak found using the using block correlation scheme may only be the peak within the predefined correlation window, but not the actual peak between the reference frame and the compare frame. In other words, the block correlation scheme may be efficient in tracking the movement of the optical input device but there is still room for improving the tracking accuracy.